One weakness that most early electronic
calculators had was that the vast majority of them utilized some type of
visual display device, examples being Nixie tubes, gas-discharge tubes and
panels, CRT displays, vacuum-fluorescent tubes, and incandescent
indicators. The problem with all of these indication technologies
was the lack of hardcopy output. For this reason, some realms of
calculating that could benefit from the speed of electronic calculators
actually kept on using their "old" electro-mechanical printing calculating
machines. Why? While slow and rather noisy, these mechanical
calculators provided a permanent record of their calculations. For financial
institutions, accountants, and bookkeepers, a hard-copy that could be saved
as a check of the math performed was a very important requirement.

Calculators that use a visual display
to indicate their answers had the disadvantage that results had to be manually
copied onto some form of permanent record, making the chance for human
transcription error much greater than a calculator that provided a
printed output. A means had to be developed for an electronic
calculator to be married to some type of printing technology to provide
the best of both worlds...electronic speed, and hardcopy output. One of
the biggest challenges was building a printing mechanism that had sufficient
speed to minimize the impact on the speed of the electronics, and wasn't so
expensive that it priced the machines out of the market.

While Friden had great success with
their first-generation electronic calculators, the
Friden EC-130
and Friden EC-132,
it was clear that a segment of the market
wasn't buying into calculators with electronic displays. There were a few
electronic printing calculators on the market at the time, such as the
Monroe EPIC 2000 and
EPIC 3000, and the amazing
Mathatronics Mathatron, but these machines were
expensive, high-end machines with scientific functions and programmability.
Wang offered printing peripherals for their calculators, but, like the Monroe
and Mathatronics machines, these machines offered functionality way beyond
the needs of basic business accounting. Bankers and accountants weren't
interested in paying the extra money for these advanced features when
they would never be used. Wanderer Werke in Germany had developed a fairly
advanced programmable electronic printing calculator, but their market was mainly
in Europe. Friden needed to address this market segment with a basic four function
electronic calculator that made a printed record of its calculations.

Friden 1152 Internals

The Friden 130 and 132 were becoming
a bit dated by 1966. The machines were large, heavy, relatively slow, and
expensive compared to some of the newer calculators that were showing up
in the rapidly expanding marketplace. Robert Ragen, the brilliant engineer
that designed the Friden 130 and 132 calculators, had designs in mind that
would utilize the same basic architecture of the 130/132 transistorized
calculators, but would implement the logic using the new technology of
small-scale integrated circuits. An IC-based design would save space and
weight, along with reducing power consumption. Such savings make the
machines less expensive to manufacture due to reduced parts count and complexity.
Ragen set about developing designs for two lines of calculators that would
share the same general design, differing only in their means of communicating
results to the user. One line of machines would utilize a CRT-display,
similar to the 130/132 calculators, and the other line would consist of
printing calculators.

A new idea would also be implemented
in some models within each line -- simple programmability. Users who
frequently ran repetitive calculations could use this feature to automate
the calculations, making only variable entry required by the user,
with the calculator carrying out the "learned" sequence of mathematical
operations automatically. To Ragen, the addition of printing capability,
along with the added utility of programmability, seemed to be just what
the market needed to address the shortcomings of the earlier calculators.

Model Identification on Back Panel (note massive heatsink)

The problem was, even though these
new designs implemented great new features, what the market really wanted
was less-expensive basic calculators. The downside with the second
generation Friden machines was that they ended up being rather expensive
to manufacture. The printing calculators used a complicated print mechanism
that was expensive to manufacture. The CRT-display machines used costly
cathode-ray tubes for display, which required specialized circuitry to drive.
Japanese manufacturers were sticking with tried-and-true display technologies,
and though they didn't market printing calculators at the time, the cost of
their machines was significantly less expensive due to inexpensive labor
in Japan, extremely efficient manufacturing processes, and their use of
well-established technology.

Even though the market seemed like
it needed the features of Ragen's new designs, the monetary bottom line was
really the driving factor behind the broad marketplace. Singer's management, in
a quest to address the fact that the market demanded lower-cost calculators,
forged a partnership with Japanese electronics giant (and calculator
manufacturer) Hitachi. This relationship spelled the beginning of the
end of Friden's in-house electronic calculator development.

The first calculator to come out of
the Hitachi relationship was the Friden 1112,
which actually was marketed by Singer/Friden before Ragen's second-generation
calculator designs were complete. The development of Ragen's new series
of machines continued while the 1112 was being marketed, but it soon became
clear that the broad market was willing to forego printing and
programming functions just to have an electronic calculator that was
comparatively inexpensive. The 1112 was a good market success, proving
to Singer's management that their hunch was right. However, by the time
all of this came to light, Ragen's designs were nearing production reality.
Rather than cancel the project and lose the investment in the
development of the machines, it was decided to go ahead and bring the machines
to market to try to recapture some of the development costs.
The resulting calculators became the Friden 115x-series of printing
electronic calculators, and the Friden 116x-series (See the exhibit on the
Friden 1162 for more information on the
116x-series calculators.) of CRT-display calculators -- the last calculators
designed and manufactured by what was left of Friden Calculating Machine Co.

Model/Serial Number Tag

These two lines of calculators all
share a similar architecture to the Friden 130/132 machines, utilizing the
same four-level RPN stack arrangement, pulse-train digit representation,
counter-based arithmetic unit, fixed decimal, and magnetostrictive delay
line for working register storage. DTL (Diode-Transistor Logic) and early TTL
(Transistor-Transistor Logic) small-scale integrated circuits are utilized for
the logic of the machines, significantly reducing the size and weight
of the calculators compared to the 130/132, and allowed additional
functionality. The Friden 115x-series calculators were Friden's answer
to the perceived need for a printing calculator. The Singer/Friden 1152
calculator exhibited here is the high-end machine in the original line,
providing four functions, thirteen digit capacity, automatic square root,
a single store/recall memory register, and 30-step programmability. Three
other calculators made up the initial group of machines in the 115x-series.
The 1150, the first calculator introduced in the
115x-series, provided the basic four math functions and single memory
register, with no programming capability.
The 1151 was a 30-step programmable version
of the 1150. The difference between the 1151 and 1152 is that the 1151
does not have a square root function. Lastly, the 1154 was a non-programmable
four function machine squarely targeted at the business market, removing
two stack manipulation functions (Duplicate and Exchange), and replacing
them with sum and difference of product functions. Two later machines were
added to the 115x-series, though they were architectually very different than
the other machines in the series. The Friden 1155 and 1155A were full
scientific calculators, with much more comprehensive programming capabilities,
and significantly more memory registers. The machines utilized large-scale
integrated circuit technology, eliminating the need for the magnetostrictive
delay line. The only common components between the 1155/1155A and the other
machines in the 115x series were the cabinetry and printing mechanism.
The 1155 provided 20 memory registers, and the 1155A provided
100 memory registers.

The original 115x-series calculators
appear to have debuted sometime in late 1968. The example exhibited here
was manufactured in early 1970, based on date codes on the integrated circuits
in the machine. These calculators were among the earliest American-made
calculators to use integrated circuits. The Japanese had been marketing
calculators utilizing bipolar and early MOS (Metal Oxide Semiconductor)
integrated circuits as early as 1966. For whatever reason, American
calculator manufacturers were a bit slow to adopt integrated circuit
technology, with some American manufacturers
(such as Wang and Hewlett Packard) not introducing integrated circuit-based
calculators until the early 1970's.

Like Ragen's previous designs, the 1152 utilizes a four register
RPN (Reverse Polish Notation) stack architecture. The four registers
are connected in such a way that new entries are placed into the
'bottom' register of the stack. Numbers that go off the 'top' of the
stack are lost. The [FIRST NMBR/PRINT] key completes entry of a number,
preparing the machine for entry of the next number. As soon as the first digit
of the next number is entered, the stack is 'pushed' up one level, and
the new number is entered into the bottom of the stack. Addition, subtraction,
multiplication, and division operate on the bottom two registers of the stack,
'popping' the stack down one level, leaving the result in the bottom register
of the stack. The square root operation calculates the square root of
the number in the bottom register of the stack, leaving the result in the
argument's place, without disturbing the stack.

The Control Panel (including stack status indicator) of the Friden 1152

Given the lack of a display on the 115x-series calculators, a novel means
for indicating the status of the RPN stack was developed. In fact, the concept
was unique enough to patent. An indicator on the front panel of the
115x-series calculators shows the status of the stack. The indicator
has four incandescent lamps stacked in a vertical configuration, behind
a red plastic lens. If a register in the stack contains non-zero content,
the corresponding indicator lights. For example, if the bottom and
next-to-bottom register contain numbers, the bottom two indicators will
be lit. Carl Herendeen, another of Friden's prolific engineers, developed
the idea for this status display, and was granted US Patent #3495221 in
February of 1970.

Three stack manipulation functions are provided. The [I] key exchanges
the bottom two registers on the stack, and the [DUP] key pushes the stack up
one level, duplicating the number of the bottom of the stack. The [FIRST
NMBR/PRINT] key actually has three functions. The first function,
entering a number into the stack, was documented earlier.
If pressed after a math operation, the [FIRST NMBR/PRINT] key will print
the content of the bottom register on the stack. If pressed a second time,
all four registers on the stack are printed, one register per line, with the
"top" stack register printed first, and the "bottom" register last.
The [ENTRY/CLEAR STACK] key is another dual-function key, with the first
press clearing the bottom register of the stack, useful for erasing
erroneous entries. If pressed a second time, the entire stack is cleared.
In both cases, the content of the memory register is not affected.

The Keyboard of the Singer/Friden 1152

The memory register of the 1152 is a simple store/recall register.
Pressing the [TO MEMORY] key takes the number on the bottom of the stack
and copies it to the memory register, popping the stack downward.
The [FROM MEMORY] key causes the content of the memory register to be
pushed into the bottom register of the stack.

The programming features of the 1152 are rather unique. The machine
only stores function key presses. Numeric entries are not stored as steps
in the program memory. The concept of programmability for these
machines is intended only for simple linear operations. These machines
were not designed for solving complex problems through their programming
capability. The inability to store constants as part of a program
seriously limits the complexity of problems the machines can address.
The programming feature of the 1151 and 1152 was intended for automating
simple, repetitive types of calculations -- for example, performing
discount or mark-up calculations in a retail operation, or calculating the
area of circles for an engineering application.

The programming functions are controlled by three keys.
The [LEARN] key, which locks down when pressed, puts the calculator
into learn mode. In this mode, the calculator operates as normal, but
each operation key ([FIRST NMBR/PRINT], [+], [-], [X=], [÷=], [I], [DUP], [TO MEMORY],
[FROM MEMORY], and [AUTO]) is stored upon entry into
the delay line, and then executed as usual. The steps are stored in
the delay line as single-digit
numbers, much like normal numeric entry, but by virtue of their location in the
delay line, they
are interpreted as instructions when played back. The [AUTO] key has a
special meaning when recorded in LEARN mode; when this code is encountered
while a program is being run, the calculator stops and waits for user
input, allowing the user to enter variable data. The [PROG RESET] key
clears learn mode (releasing the [LEARN] key), and begins execution of the
just-entered sequences of operations. The [AUTO] key resumes execution when
the machine stops awaiting variable data from the user. It should
be noted that while the 1152 has a square root function, it is not possible
to use the square root operation within a program. If the square root key
is pressed in LEARN mode, the function will be performed, but it will not
be stored in the program memory. This is because there are only ten possible
operation codes that can be stored in the program memory, and all ten
codes are used by the basic functions of the machine. For more information
on programming the 1152, see the
1151 Programming Instructions manual (programming on the 1152 is identical
to that on the 1151.)

Example of Printed Output from Friden 1152 with Annotation

The printing mechanism of the 115x-series calculators is quite amazing.
The design of the mechanism was developed by Friden engineers Leland D.
Chamness and Andre F. Marion, who were granted US Patent #3406625 in
October of 1968 for the design. Given Friden Calculating Machine Company's
famous mechanical and electro-mechanical calculators, it is no surprise that
the printing mechanism is a prime example of the mechanical brilliance of
Friden's engineers. Sadly, the design for the printer was one of the last
calculator-related mechanical masterpieces developed by Friden's engineers
after Singer's acquisition of Friden in 1963 eventually eliminated in-house
design of calculators. Interestingly, as late as 1970, the Friden
division of Singer Corp. was offering
the same basic printer mechanism for sale as a Digital Printer module.
The unit included all of the drive and amplifier electronics, making it a
relatively simple device to interface to. The 11-pound, 11-3/4" wide by
7-5/8" high by 8-3/4" deep device sold in single quantities for $450.

The printer used in the 115x-series calculators is a serial (character
at a time) impact printer. Unlike most other printing calculators of the
1970's, which use a drum with multiple columns of embossed digits,
and a like number of hammers to print a line at a time
(see the exhibit on the Wang 600 for
an example of this type of printing technology), the serial means of
printing used on the Friden 115x-series calculators is quite unique.
Interestingly enough, this design lives on, as many of today's small
desktop printing electronic calculators use a printing mechanism based
on this design.

Printer Mechanism Diagram (from US Patent #3623009)

The printing mechanism consists of a carriage containing a print wheel
that is embossed with symbols around its periphery. The
print wheel can move horizontally on a shaft that rotates, turning
the print wheel at high speed. The symbols embossed on the print wheel
are arranged in two groups. The first group consists of the digits zero
through nine and the decimal point. The second group contains function
indicator characters, ("+", "-", "=", "C", "F", "X", "M", "E" and "÷").
The carriage carrying the print wheel also carries a solenoid-activated
hammer, located behind the print wheel. The hammer is situated such that
when the solenoid is activated, the hammer moves towards the print wheel
to strike it.

The print wheel showing detail of the embossed numeric section

The carriage is mounted on a slide such that the printing
mechanism can move back and forth horizontally. A helically grooved shaft
is located below the carriage. The grove in the shaft is machined into
it in such a way that when the carriage is mechanically coupled to
the shaft, the carriage will be pulled horizontally (to the left) as the
shaft rotates. A solenoid-activated pin in the carriage engages the
groove in the shaft to allow the carriage to be carried to the left from
the home position (located at the rightmost end of the paper) when the
solenoid is energized. When the solenoid is released, a spring causes
the carriage to quickly return to the home position. The paper to be
printed upon is situated such that it is interposed between the print
wheel and the hammer.

OEM Replacement Ink Roller

A special replaceable inked roller cartridge
(Singer part number 811490) provides a supply of ink, which is transferred
to another special rubber roller that rides against the print wheel to keep
the embossed characters on the periphery of the print wheel consistently
coated with a layer of ink. A toothed metal wheel is connected to the left
end of the shaft that rotates the print wheel. The teeth on this wheel are
positioned such that they correspond to the characters embossed on the print
wheel. As the wheel spins in synchronism with the printwheel, the teeth of the
wheel trigger small pulses of current in a series of three coils located
in close proximity to the toothed wheel. One coil pulses as the number
section of the print wheel is nearing position, another pulses when the
symbol section of the print wheel is nearing position, and the last coil
pulses as each character on the print wheel is positioned so that the hammer
can strike it to cause the character to print. The pulses coming out of these
coils tell the electronics that drive the printer which character (be it digit
or function symbol) is currently aligned with the print hammer.
As the carriage travels across the paper right to left, the signals coming
from the printwheel position sensors trigger the hammer solenoid to fire at the
correct instant to cause the various digits and symbols to be printed
on the paper, character at a time. Once an entire line of characters
has been printed, the carriage is released and returns to the home position,
and a clutch activates to cause the paper to advance one line, readying
the printer for the next printing cycle. A single high-torque electric
motor, rotating at approximately 3600 RPM, provides the rotational energy
that operates the entire print mechanism. The motor is only powered up when
printing (or paper feed) is occurring, limiting the noise of a motor running
continuously. The 1152 is rather noisy while printing, with the noise
of the motor combining with the 'clackity-clack' of the print hammer.
The printer prints at the surprisingly fast rate of 37 characters per second,
resulting in an average rate of 1-1/2 lines per second. This speed allows
the calculator to have the benefits of the speed of electronic circuitry,
while still providing a hard copy of the calculations. Given that the
special keyboard of the 115x-series calculators locks while calculations
are in progress (including the time it takes to print a result), it is not
possible for a skilled operator to 'get ahead' of the machine. Digits in
front of the decimal point are printed in groups of three for easier reading.
For example, the number 123456.789 would be printed as '123 456.789'.
A pushbutton on the top of the cabinet activates the paper feed mechanism
to allow the paper to be advanced by the user.

The Printer Drive Circuitry

A circuit board mounted on the left end of the printer mechanism contains
the circuitry for conditioning the print position sensor pulses, as well as
drivers for the various solenoids that operate the printing mechanism.

One of the six circuit boards in the Friden 1152

Most of the integrated circuits in the 1152 are made by Texas Instruments,
with a few chips from other vendors (Motorola, Fairchild and National
Semiconductor) sprinkled in here and there. The machine is made up of a
mix of very early 7400-series TTL IC's (mostly 7474 dual flip-flops), along
with Texas Instruments Small-Scale DTL (Diode-Transistor Logic)
devices in the SN158xx series. Along with the small-scale logic,
the 1152 (as well as other machines in the 115x and 116x lines) use a three
chip medium-scale integration device (likely DTL) made by Texas Instruments.
The chipset consists of SN1286, SN1287, and SN1288 devices. Each device
implements one of the counters in the "three counter" arithmetic unit
of the machine. The method of using counters (rather than adders) to perform
the arithmetic came from the original Friden EC-130 calculator. In the
original EC-130 design, four counters were used to count pulses in order
to carry out math operations. As time went on, it was realized that three
counters could perform the same function, so design changes were made to the
EC-130 and EC-132 calculators to eliminate one of the counters, reducing
component count (and thus cost). This arithmetic architecture was quite
efficient, and was carried over to the 115x/116x-series calculators, with
the implementation of the counters done in integrated circuit form.

The Printed Circuit Backplane of the Friden 1152

The 1152 uses a total of 166 integrated circuits, along with a significant
compliment of transistors, diodes, resistors and capacitors. The main
logic of the machine is spread across six circuit boards that are plugged in
vertically in a hefty aluminum card cage located toward the rear of the chassis.
The circuit boards plug into a backplane made from a printed circuit board,
which connects to other areas of the calculator (power supply, keyboard,
printer, status indicators) via wires soldered to the pins of the edge
connector sockets. The circuit boards in the machine are made of high
quality fiberglass construction, with gold-plated edge connector fingers.
The boards have traces on both sides, with plated-through feedthroughs to
provide connections between traces in opposing sides. Each circuit board
is approximately 9 1/4" by 5 1/4", and has two groups of edge connector fingers,
consisting of 44 pins per group (2 x 22), for a total of 88 pins.

Power supply circuitry of the 1152

The power supply of the 1152 is a basic linear supply, using a transformer
to step line voltage down to various AC voltages, which are then rectified,
filtered, and regulated to make up the various DC voltages used in the
calculator. The power supply is split up in a number of areas within the
machine. A main power supply board is mounted alongside the printer
assembly that contains some of the voltage regulation circuits, as well as
the large electrolytic capacitors that provide filtering. Another small
board located near the delay line in the base of the machine provides some
of the specialized voltages needed by the delay line. The two transformers
that step down line voltage are mounted to the chassis. Lastly, the large
power transistors and high-wattage resistors that dissipate significant
amounts of heat are secured to the large heatsink that makes up the back
panel of the machine.

The Delay Line (in aluminum housing) Assembly in the base of the Friden 1152

Though IC's had replaced the all-transistor electronics of the
earlier 130/132 machines, the 1152 still uses acoustic delay line technology
for storing the working registers of the machine. The delay line
of the 1152 is contained in an aluminum housing in the bottom of the
machine, as in the 130/132. At the time, even integrated
circuits did not have sufficient capacity to represent all of the
working registers of the machine. The acoustic (magnetostrictive) delay
line was a tried and true, along with inexpensive way to provide sufficient
storage capacity for the calculator. The delay line in the 1152 contains
a total of six registers, designated RS, R0, R1, R2, R3, and R4. RS is
the memory register, R0 is a special register used by the printing system,
and R1 through R4 are the four registers of the RPN stack. Each register
can hold the representation of 25 digits, with an additional digit location
(for a total of 26) reserved as a marker to tag the beginning of a register
in the bit stream. Each digit is represented by a number of pulses.
No pulses during a given digit time represent the digit zero. Nine
pulses represents the digit nine. Each digit time is divided into 16 slots,
each of which can be filled with a pulse (essentially a '1' bit) or no
pulse (a '0' bit). As a result, each register consists of 26 X 16 bits,
or 415 bits. With six registers stored in the delay line that makes a
total of almost 2500 bits. You may note that each register has 25
possible digits, but the capacity of the machine is only 13 digits.
A total of 15 digit positions store a number in the machine, with two
digit positions consumed by codes that indicate the location of the
decimal point within the number, and another code that indicates the sign
of the number. The remaining 10 digit slots of R4, R3, and RS make up
the 30-step program store for the programming feature of the calculator.
The 'spare' digits of R0, R1, and R2 are not used, but still circulate
through the delay line.

The 1152 calculates at the same basic rate as its CRT-based
relative, the Friden 1162. All 9's divided by
1 takes just over one second to complete (not including printing time).
Square root operations take an amount of time based on the number of
digits in the argument, with calculation times ranging from about 0.25
seconds to almost 1.5 seconds. Printing occurs as soon as the calculation
completes. During the calculations, the stack status indicators flicker
a bit, then settle into the correct configuration once the calculation
completes.

The cabinet of the 115x-series calculators consists of a heavy cast aluminum
base, with a stamped metal removable grille covering the bottom of
the base to allow service technicians access to the adjustments for delay
line timing. The upper portions of the cabinet are also made of cast aluminum.
The keyboard bezel is made of a plastic casting. The front panel of the
machine is a cast-plastic insert which was available in four different colors
to fit in with office environment decor. This insert was available in
Slate, Aqua, Olive, or Terracotta. The machine exhibited here
has the Terracotta-colored insert.

Front Panel Insert in "Olive" Color

Division by zero results in the machine aborting the calculation, printing
an "E" in the rightmost-column and clearing the stack. Overflow causes the
same behavior. Extracting the square root of a negative number does not
flag an error. The calculator returns the answer as if the argument was
positive.